But yeah, I mean, I see the predictable factors as

1. Your GPU's hash rate
2. The block reward
3. Time taken to block
4. Difficulty

And I see the unpredictable factors as

1. altcoin to BTC price
2. BTC to USD price

I do think, though, that the higher the volume of an altcoin, the more stable the value is going to be.

More BTC volume for an altcoin means that it takes  more people and more money to shift the coin's value, thus making the value more stable.